The present invention relates to a display device, and more particularly to a display device and a manufacturing method of the same which can enhance reliability thereof by preventing the degradation of characteristics of thin film transistors attributed to the diffusion of an aluminum element into a polysilicon layer during a heating step when an aluminum-based conductive layer is used as a wiring electrode which is brought into contact with the polysilicon layer.
A panel type display device adopting an active matrix method which uses active elements such as thin film transistors or the like (explained hereinafter as thin film transistors) includes pixel regions and peripheral circuits such as driving circuits which are formed in the periphery of the pixel regions. In the thin film transistor which uses an aluminum-based conductive layer as source/drain electrodes thereof, there has been known a thin film transistor in which a molybdenum nitride film is stacked above or below the aluminum electrode layer as a conductive layer forming an electrode which comes into contact with a polysilicon layer and a cross-sectional shape of wet etching is controlled at the time of performing patterning (see JP-A-9-148586). Further, there has been also known a thin film transistor in which a molybdenum film or a titanium nitride film is stacked on both of upper and lower surfaces of an aluminum electrode layer and a cross-sectional shape of the wet etching is controlled in the same manner as the above-mentioned thin film transistor (see JP-A-2000-208773). However, in both of these patent literatures, no consideration has been made with respect to the degradation of the thin film transistor attributed to the diffusion of the aluminum element into the polysilicon layer.